For one, researchers can compare the mouse genome to the human genome. Comparing the genomes of different organisms is a burgeoning field of science called comparative genomics.

The Mouse Sequencing Consortium, made up of government researchers as well as scientists from Merck, SmithKline Beecham and Affymetrix, found that the mouse genome has about 3.1 billion chemical letters of DNA, about the same as humans.

Researchers all over the world are mapping the genome sequences of the chimp, mouse, rat, fruit fly, nematode worm and at least two types of pufferfish to hold it up to the human genome in an attempt to discover the secrets of evolution and disease.

"Comparing mouse sequence to human sequence will help identify previously unknown human genes, in essence using evolution's 'lab notebook' to understand how the genome works," said Francis Collins, director of the National Human Genome Research Institute, in a statement.

By comparing the genomes of different creatures, researchers can pinpoint which genes have survived hundreds of millions of years of evolution. And one of the best ways to find important genes is to find those that have survived.

Researchers are also interested in the mouse because so many biological studies have been done using it. Because it's a mammal, it is in many ways genetically close to humans.

But it's also distant enough that scientists can easily notice similar patterns in gene sequences between mice and humans. These genes, researchers say, are undoubtedly functionally important because they have survived the evolutionary time between mouse and man.

Different aspects of biology call for different species to compare with the human, researchers say. Different genes are the best for getting information about different conditions.

Merck has already used the data to find a mouse equivalent of a human gene that they believe is related to schizophrenia. The discovery will help the company develop a mouse model to study the gene's association with the disease.

In April, Celera Genomics, the company that created its own map of the human genome, said it had completed an assembly of the mouse genome, but that they would not publish their data in a scientific journal. Only those who pay for a subscription to Celera's databases will have access to it.